Billy Graham is pretty much dead. It's not nice to say, but there you have it. Franklin does not have the same star power that his dad does and, besides, they're Protestants so a hereditary Protestant Pope is not Franklin's to claim.
Therefore, there is an opening for American Protestant Pope and Rick Warren covets the title. He wants to be the moral voice of the moral majority the way Graham used to be and he has a bigger ego to boot. So he's happy to lay his hands on the new President and have the media give him the legitimacy the media once gave Billy Graham. That the new President is a proponent of infanticide is irrelevant to his resume.
Win - win. He's not compromising his principles. He's just giving legitimacy to get legitimacy.
And unlike Billy Graham, Rick Warren is fully committed to the pro-life cause.
P.S. - It also really does hack off all the right people. Much like the LaHood pick will when people remember he sat in the Speaker's Chair presiding over Clinton's impeachment.
P.P.S. - Unfortunately, I find Rick Warren insufferable. He's a book salesman more than an evangelist and does not have the life experiences Graham had that taught Graham humility.